Multi-piece solid golf ball

ABSTRACT

A golf ball is provided that achieves a satisfactory distance on full shots with a driver and an iron, is superior in the short game, and has a good feel at impact and a good durability. The golf ball has a core formed of a rubber composition as one or more layer, an inner envelope layer formed of a resin material as one or more layer, an outer envelope layer and intermediate layer which are each formed of a resin material as one layer, and a cover formed of a resin material as one layer having a thickness of not more than 1.0 mm. The inner envelope layer-encased sphere, outer envelope layer-encased sphere, intermediate layer-encased sphere and ball have Shore C hardnesses at the respective surfaces thereof which together satisfy certain conditions, and the ball has at least a given deflection under specific loading conditions.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2020-127860 filed in Japan on Jul. 29,2020, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a multi-piece solid golf ball composedof five or more layers that include a core, one or more inner envelopelayer, an outer envelope layer, an intermediate layer and a cover.

BACKGROUND ART

Many innovations have been made in designing golf balls with amultilayer construction, and numerous balls that satisfy the needs ofnot only professional golfers, but also skilled and mid-level amateurgolfers, have been developed to date. For example, functionalmulti-piece solid golf balls in which the hardnesses of the respectivelayers—i.e., the core, envelope layer, intermediate layer and cover(outermost layer)—have been optimized are in wide use. Also, a number oftechnical disclosures have been published that focus on the hardnessprofile of the core which accounts for most of the ball volume and, bycreating various core interior hardness designs, providehigh-performance golf balls for professional golfers and mid-level toskilled amateur golfers.

Examples of such literature include JP-A 2009-095364, JP-A 2016-101254,JP-A 2009-095358, JP-A 2016-101256, JP-A 2008-149131, JP-A 2009-095365and JP-A 2009-095369. These disclosures, all of which relate to golfballs having a multilayer construction of four or five layers, focus on,for example, the hardnesses and the thicknesses of the respectivelayers—namely, the core, the envelope layer, the intermediate layer andthe cover (outermost layer), and the core hardness profile.

However, there remains room for improvement in optimizing the hardnessprofile of the core and the thickness relationship among the layers inthese prior-art golf balls. That is, these golf balls, even if they areable to retain a good distance on driver (W #1) shots, often fall shortin terms of their distance on iron shots. Moreover, with some of theseprior-art golf balls, when an attempt is made to obtain a superiordistance performance not only on driver shots but also on iron shots, asufficiently high spin rate on approach shots cannot be achieved,resulting in a ball that lacks a high playability or that has a lessthan satisfactory feel at impact on full shots. Accordingly, thereexists a desire for a golf ball which, as a distance ball, not onlyachieves an increased distance on driver shots but also provides animproved distance on iron shots, which has a good feel at impact and agood durability, and which moreover has a good playability in the shortgame.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide amulti-piece solid golf ball which, along with achieving a satisfactorydistance on full shots not only with a driver (W #1) but also with aniron, is receptive to spin on approach shots and thus superior in theshort game, provides a feel at impact that is soft and good, andmoreover has a good durability to cracking on repeated impact.

As a result of extensive investigations, I have found that the aboveobject can be achieved in golf balls having a core, an inner envelopelayer, an outer envelope layer, an intermediate layer and a cover byforming the cover so as to be relatively soft, forming the intermediatelayer so as to be relatively hard, and also forming the outer envelopelayer adjoining the inner side of the intermediate layer so as to besofter than the intermediate layer and harder than the surface of theinner envelope layer. That is, I have discovered that by forming thecore of a rubber composition as one or more layer, forming the innerenvelope layer of a resin material as one or more layer, forming theouter envelope layer of a resin material as one layer, forming theintermediate layer of a resin material as one layer and forming thecover of a resin material as one layer having a thickness of not morethan 1.0 mm, by setting the hardness relationship among the layers suchthat the Shore C hardness at the surface of the inner envelopelayer-encased sphere, the Shore C hardness at the surface of the outerenvelope layer-encased sphere, the Shore C hardness at the surface ofthe intermediate layer-encased sphere and the Shore C hardness at theball surface satisfy the conditions (Shore C hardness at surface ofouter envelope layer-encased sphere)>(Shore C hardness at surface ofinner envelope layer-encased sphere) and (Shore C hardness at surface ofintermediate layer-encased sphere)>(Shore C hardness at ball surface)and moreover by conferring the ball with a deflection when compressedunder a final load of 1,275 N (130 kgf) from an initial load of 98 N (10kgf) of at least 3.0 mm, a good distance can be obtained on full shotswith a driver (W #1) and an iron owing to a spin rate-lowering effectand a soft and good feel can be obtained at impact, in addition to whichthe durability to cracking on repeated impact and the controllability ofthe ball around the green are both good.

In other words, the golf ball of the invention is a ball which has fiveor more cover layers and provides additional controllability around thegreen. This ball ensures a satisfactory distance owing to the spinrate-lowering effect on full shots with both a driver (W #1) and aniron, and is characterized by having an especially superior distance oniron shots. In addition to ensuring a good distance, the inventive ballis receptive to spin in the short game and thus also satisfies the needsof users who desire controllability around the green. Moreover, a softand good feel can be obtained on all shots with this ball.

Accordingly, the invention provides a multi-piece solid golf ball havinga core, an inner envelope layer, an outer envelope layer, anintermediate layer and a cover, wherein the core is formed of a rubbercomposition as one or more layer, the inner envelope layer is formed ofa resin material as one or more layer, the outer envelope layer isformed of a resin material as one layer, the intermediate layer isformed of a resin material as one layer and the cover is formed of aresin material as one layer having a thickness of not more than 1.0 mm.The Shore C hardness at the surface of the sphere obtained by encasingthe core with the inner envelope layer (inner envelope layer-encasedsphere), the Shore C hardness at the surface of the sphere obtained byencasing the inner envelope layer-encased sphere with the outer envelopelayer (outer envelope layer-encased sphere), the Shore C hardness at thesurface of the sphere obtained by encasing the outer envelopelayer-encased sphere with the intermediate layer (intermediatelayer-encased sphere) and the Shore C hardness at the surface of theball together satisfy the conditions (Shore C hardness at surface ofouter envelope layer-encased sphere)>(Shore C hardness at surface ofinner envelope layer-encased sphere) and (Shore C hardness at surface ofintermediate layer-encased sphere)>(Shore C hardness at ball surface).Also, the ball has a deflection when compressed under a final load of1,275 N (130 kgf) from an initial load of 98 N (10 kgf) of at least 3.0mm.

In a preferred embodiment, the golf ball of the invention satisfies thecondition:

1.0≤(OE vh+IE vh)/Core vh≤4.5,

where Core vh is the product of the core volume (mm³) multiplied by theShore C hardness Cm at the midpoint between the core surface and thecore center, IE vh is the product of the inner envelope layer volume(mm³) multiplied by the Shore C hardness at the surface of the innerenvelope layer-encased sphere, and OE vh is the product of the outerenvelope layer volume (mm³) multiplied by the Shore C hardness at thesurface of the outer envelope layer-encased sphere.

In another preferred embodiment of the invention, the ball satisfies thecondition:

2.5≤C−B≤5.0,

where C is the deflection of the core in millimeters when compressedunder a final load of 1,275 N (130 kgf) from an initial load of 98 N (10kgf) and B is the deflection of the ball in millimeters when compressedunder a final load of 1,275 N (130 kgf) from an initial load of 98 N (10kgf).

In yet another preferred embodiment, the surface hardnesses of therespective layers satisfy the condition:

(Shore C hardness at ball surface)<(Shore C hardness at surface ofintermediate layer-encased sphere)>(Shore C hardness at surface of outerenvelope layer-encased sphere)>(Shore C hardness at surface of innerenvelope layer-encased sphere)>(Shore C hardness at core surface).

In still another preferred embodiment, the layers have respectivethicknesses which together satisfy the condition:

(cover thickness)<(intermediate layer thickness)≤(total thickness ofenvelope layer).

In a further preferred embodiment, the layers have respectivethicknesses which together satisfy the condition:

(total thickness of envelope layer)/(cover thickness+intermediate layerthickness)≥1.0.

In a still further preferred embodiment, the ball has an initialvelocity of at least 76.8 m/s.

In another preferred embodiment, the core has a diameter and the ballhas a diameter which together satisfy the condition:

0.65≤(core diameter)/(ball diameter)≤0.80.

In yet another preferred embodiment, the core has an internal hardnesswhich satisfies the condition:

(Cs−Cm)/(Cm−Cc)≥1.1,

where Cc is the Shore C hardness at a center of the core, Cs is theShore C hardness at the core surface, and Cm is the Shore C hardness atthe midpoint between the core surface and the core center.

Advantageous Effects of the Invention

The multi-piece solid golf ball of the invention can achieve a gooddistance on full shots with a driver (W #1) and an iron, and has a softand good feel. In addition, the durability to cracking on repeatedimpact and the controllability around the green are both good. The ballis particularly outstanding in terms of the distance traveled on shotswith an iron.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 is a schematic cross-sectional view of a multi-piece solid golfball according to the invention which has a five-layer construction.

FIGS. 2A and 2B are, respectively, a top view and a side view of theexterior of a golf ball showing the arrangement of dimples common to allof the Examples and Comparative Examples described herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description taken in conjunctionwith the appended diagrams. Referring to FIG. 1, the multi-piece solidgolf ball of the invention is a golf ball G of five or more layers whichhas a core 1, an inner envelope layer 2 a and outer envelope layer 2 bencasing the core 1, an intermediate layer 3 encasing the envelope layer2, and a cover 4 encasing the intermediate layer 3. Numerous dimples Dare typically formed on the surface of the cover 4. Although not shownin the diagrams, a coating layer is generally painted onto the surfaceof the cover 4. Aside from the coating layer, the cover 4 is positionedas the outermost layer in the layered construction of the golf ball.Both the core 1 and the inner envelope layer 2 a are not limited to asingle layer, and may each be formed as two or more layers. However, theouter envelope layer 2 b, the intermediate layer 3 and the cover 4 areeach formed as a single layer.

The core has a diameter that is preferably at least 24.7 mm, morepreferably at least 25.7 mm, and even more preferably at least 26.7 mm.The upper limit in the core diameter is preferably 34.7 mm or less, morepreferably 33.3 mm or less, and even more preferably 31.7 mm or less.

The (core diameter)/(ball diameter) ratio is preferably at least 0.65,more preferably at least 0.67, and even more preferably at least 0.70.The upper limit is preferably not more than 0.80, more preferably notmore than 0.76, and even more preferably not more than 0.73. When thisvalue is too small, the initial velocity of the ball may be low or thedeflection hardness of the overall ball may rise, which may result in anincreased spin rate on full shots and make it impossible to achieve theintended distance. On the other hand, when this value is too large, thespin rate on full shots with an iron may rise and make it impossible toachieve the intended distance, or the durability to cracking on repeatedimpact may worsen.

The core has a deflection when compressed under a final load of 1,275 N(130 kgf) from an initial load of 98 N (10 kgf) which, although notparticularly limited, is preferably at least 5.0 mm, more preferably atleast 5.5 mm, and even more preferably at least 6.0 mm. The upper limitis preferably not more than 9.0 mm, more preferably not more than 8.5mm, and even more preferably not more than 8.0 mm. When the coredeflection is too small, i.e., when the core is too hard, the spin rateof the ball may rise excessively so that the ball does not travel far,or the feel at impact may become too hard. On the other hand, when thecore deflection is too large, i.e., when the core is too soft, the ballrebound may become too low so that the ball does not travel far, thefeel at impact may become too soft, or the durability to cracking onrepeated impact may worsen.

The core is obtained by vulcanizing a rubber composition composedprimarily of a rubber material. This rubber composition is typicallyobtained by using a base rubber as the chief component and compounding,together with this, other ingredients such as a co-crosslinking agent, acrosslinking initiator, an inert filler and an organosulfur compound.

It is preferable to use polybutadiene as the base rubber. A commercialproduct may be used as the polybutadiene. Illustrative examples includeBRO1, BR51 and BR730 (all from JSR Corporation). The proportion ofpolybutadiene within the base rubber is preferably at least 60 wt %, andmore preferably at least 80 wt %. Rubber ingredients other than theabove polybutadiene may be included in the base rubber, provided thatdoing so does not detract from the advantageous effects of theinvention. Examples of rubber ingredients other than the abovepolybutadiene include other polybutadienes and also other diene rubbers,such as styrene-butadiene rubbers, natural rubbers, isoprene rubbers andethylene-propylene-diene rubbers.

The co-crosslinking agent is an α,β-unsaturated carboxylic acid and/or ametal salt thereof. Specific examples of unsaturated carboxylic acidsinclude acrylic acid, methacrylic acid, maleic acid and fumaric acid.The use of acrylic acid or methacrylic acid is especially preferred.Metal salts of unsaturated carboxylic acids include, without particularlimitation, the above unsaturated carboxylic acids that have beenneutralized with desired metal ions. Specific examples include the zincsalts and magnesium salts of methacrylic acid and acrylic acid. The useof zinc acrylate is especially preferred.

The unsaturated carboxylic acid and/or metal salt thereof is included inan amount, per 100 parts by weight of the base rubber, which isgenerally at least 5 parts by weight, preferably at least 6 parts byweight, and more preferably at least 7 parts by weight. The amountincluded is generally not more than 50 parts by weight, preferably notmore than 40 parts by weight, and more preferably not more than 30 partsby weight. Too much may make the core too hard, giving the ball anunpleasant feel at impact, whereas too little may lower the rebound.

It is suitable to use an organic peroxide as the crosslinking initiator.Commercially available organic peroxides may be used for this purpose.Examples of such products that may be suitably used include Percumyl D,Perhexa C-40 and Perhexa 3M (all from NOF Corporation), and Luperco231XL (from AtoChem Co.). One of these may be used alone, or two or moremay be used together. The amount of organic peroxide included per 100parts by weight of the base rubber is preferably at least 0.1 part byweight, more preferably at least 0.3 part by weight, and even morepreferably at least 0.5 part by weight. The upper limit is preferablynot more than 5 parts by weight, more preferably not more than 4 partsby weight, even more preferably not more than 3 parts by weight, andmost preferably not more than 2.5 parts by weight. When too much or toolittle is included, it may not be possible to obtain a golf ball havinga good feel, durability and rebound.

Fillers that may be suitably used include, for example, zinc oxide,barium sulfate and calcium carbonate. One of these may be used alone, ortwo or more may be used together. The amount of inert filler includedper 100 parts by weight of the base rubber is preferably at least 1 partby weight, and more preferably at least 3 parts by weight. The upperlimit per 100 parts by weight of the base rubber is preferably not morethan 200 parts by weight, more preferably not more than 150 parts byweight, and even more preferably not more than 100 parts by weight. Toomuch or too little inert filler may make it impossible to obtain aproper weight and a suitable rebound.

Commercial products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200 andNocrac MB (all available from Ouchi Shinko Chemical Industry Co., Ltd.)may be used as an antioxidant. One of these may be used alone, or two ormore may be used together.

The amount of antioxidant included per 100 parts by weight of the baserubber, although not particularly limited, is preferably at least 0.05part by weight, and more preferably at least 0.1 part by weight. Theupper limit is preferably not more than 1.0 part by weight, morepreferably not more than 0.7 part by weight, and even more preferablynot more than 0.5 part by weight. Too much or too little antioxidant maymake it impossible to achieve a suitable core hardness gradient and asuitable rebound, durability and spin rate-lowering effect on fullshots.

In addition, an organosulfur compound may be included in the rubbercomposition so as to impart an excellent rebound. Specifically, it isrecommended that thiophenols, thionaphthols, halogenated thiophenols ormetal salts of these be included. Specific examples includepentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol,p-chlorothiophenol, the zinc salt of pentachlorothiophenol, and any ofthe following having 2 to 4 sulfur atoms: diphenylpolysulfides,dibenzylpolysulfides, dibenzoylpolysulfides, dibenzothiazoylpolysulfidesand dithiobenzoylpolysulfides. The use of diphenyldisulfide or the zincsalt of pentachlorothiophenol is especially preferred.

The organosulfur compound is included in an amount per 100 parts byweight of the base rubber that is preferably at least 0.05 part byweight, more preferably at least 0.05 part by weight, even morepreferably at least 0.07 part by weight, and still more preferably atleast 0.1 part by weight. The upper limit is preferably not more than 5parts by weight, more preferably not more than 4 parts by weight, evenmore preferably not more than 3 parts by weight, and still morepreferably not more than 2 parts by weight. Including too muchorganosulfur compound may make the hardness too low. On the other hand,including too little may make a rebound-improving effect unlikely.

The core can be produced by vulcanizing and curing the rubbercomposition containing the above ingredients. For example, the core canbe produced by using a Banbury mixer, roll mill or other mixingapparatus to intensively mix the rubber composition, subsequentlycompression molding or injection molding the mixture in a core mold, andcuring the resulting molded body by suitably heating it under conditionssufficient to allow the organic peroxide or co-crosslinking agent toact, such as at a temperature of between 100 and 200° C., preferablybetween 140 and 180° C., for 10 to 40 minutes.

The core may consist only of one layer or may be formed as two layersconsisting of an inner core layer and an outer core layer. When the coreis formed as a two-layer core consisting of an inner core layer and anouter core layer, the inner core layer and outer core layer materialsmay each be composed primarily of the above-described rubber material.Also, the rubber material making up the outer core layer encasing theinner core layer may be the same as or different from the inner corelayer material. The details here are the same as those given above forthe ingredients of the core-forming rubber material.

Next, the hardness profile of the core is described. The core hardnessdescribed below refers to the Shore C hardness. This Shore C hardness isthe hardness value measured with a Shore C durometer in accordance withASTM D2240.

The core center hardness Cc is preferably at least 33, more preferablyat least 38, and even more preferably at least 43. The upper limit ispreferably not more than 62, more preferably not more than 59, and evenmore preferably not more than 54. When this value is too large, the feelat impact may harden or the spin rate on full shots may rise, as aresult of which the desired distance may not be attainable. On the otherhand, when this value is too small, the rebound may become low and theball may not travel well, or the durability to cracking on repeatedimpact may worsen.

The core surface hardness Cs is preferably at least 45, more preferablyat least 50, and even more preferably at least 55. The upper limit ispreferably not more than 74, more preferably not more than 70, and evenmore preferably not more than 66. Outside of these hardness values,undesirable results similar to those described above in connection withthe core center hardness (Cc) may arise.

The hardness Cm at the midpoint between the core surface and the corecenter is preferably at least 37, more preferably at least 42, and evenmore preferably at least 47. The upper limit is preferably not more than66, more preferably not more than 63, and even more preferably not morethan 58. Outside of these hardness values, undesirable results similarto those described above in connection with the core center hardness(Cc) may arise.

The difference between the core surface hardness (Cs) and the corecenter hardness (Cc) is preferably at least 5, more preferably at least7, and even more preferably at least 10. The upper limit is preferablynot more than 25, more preferably not more than 20, and even morepreferably not more than 15. When this difference is too small, the spinrate on full shots with a driver may rise, as a result of which thedesired distance may not be obtained. When this difference is too large,the durability to cracking on repeated impact may worsen, or the initialvelocity of the ball when struck may be low, as a result of which theintended distance may not be obtained.

The core interior hardness is such that the value of (Cs−Cm)/(Cm−Cc) ispreferably at least 1.1, more preferably at least 1.3, and even morepreferably at least 1.6; the upper limit is preferably not more than8.0, more preferably not more than 6.0, and even more preferably notmore than 5.0. When this value is too large, the durability to crackingon repeated impact may worsen or the initial velocity of the ball whenstruck may be low, as a result of which the intended distance may not beobtained. On the other hand, when this value is too small, the spin rateon full shots may rise, as a result of which the intended distance maynot be obtained.

Next, the envelope layer is described.

In the present invention, the envelope layer consists of one or aplurality of inner envelope layers and a single outer envelope layer. Inthis Specification, where mention is made of the material hardness andsurface hardness of simply the envelope layer, this refers to thematerial hardness and surface hardness of the outer envelope layer.

The inner envelope layer has a material hardness which is notparticularly limited. The material hardness on the Shore C hardnessscale is preferably at least 67, more preferably at least 70, and evenmore preferably at least 72. The upper limit is preferably not more than90, more preferably not more than 89, and even more preferably not morethan 88. The material hardness on the Shore D hardness scale ispreferably at least 43, more preferably at least 45, and even morepreferably at least 47. The upper limit is preferably not more than 60,more preferably not more than 56, and even more preferably not more than54.

The sphere obtained by encasing the core with the inner envelope layer(inner envelope layer-encased sphere) has a surface hardness which, onthe Shore C hardness scale, is preferably at least 75, more preferablyat least 78, and even more preferably at least 80. The upper limit ispreferably not more than 95, more preferably not more than 93, and evenmore preferably not more than 92. The surface hardness on the Shore Dhardness scale is preferably at least 49, more preferably at least 51,and even more preferably at least 53. The upper limit is preferably notmore than 66, more preferably not more than 62, and even more preferablynot more than 60.

The outer envelope layer has a material hardness which is notparticularly limited. The material hardness on the Shore C hardnessscale is preferably at least 67, more preferably at least 70, and evenmore preferably at least 72. The upper limit is preferably not more than90, more preferably not more than 89, and even more preferably not morethan 88. The material hardness on the Shore D hardness scale ispreferably at least 43, more preferably at least 45, and even morepreferably at least 47. The upper limit is preferably not more than 60,more preferably not more than 56, and even more preferably not more than54.

The sphere obtained by encasing the inner envelope layer-encased spherewith the outer envelope layer (outer envelope layer-encased sphere) hasa surface hardness which, on the Shore C hardness scale, is preferablyat least 75, more preferably at least 78, and even more preferably atleast 80. The upper limit is preferably not more than 95, morepreferably not more than 93, and even more preferably not more than 92.The surface hardness on the Shore D hardness scale is preferably atleast 49, more preferably at least 51, and even more preferably at least53. The upper limit is preferably not more than 66, more preferably notmore than 62, and even more preferably not more than 60.

When the material hardnesses and surface hardnesses of the respectiveenvelope layers are softer than the above ranges, the ball may be tooreceptive to spin on full shots or the initial velocity may decrease,resulting in a poor distance. On the other hand, when the materialhardnesses and surface hardnesses of the respective envelope layers arehigher than the above ranges, the feel of the ball at impact may becomehard, the durability to cracking on repeated impact may worsen, or thespin rate on full shots may rise, as a result of which a good distancemay not be obtained.

It is preferable for the surface hardness of the outer envelope layer tobe higher than the surface hardness of the inner envelope layer. Incases where one or more layer is interposed between the inner envelopelayer and the outer envelope layer, it is preferable for the ball to bedesigned in such a way that the layers become progressively harder fromthe inner envelope layer to the outer envelope layer. When such is notthe case, the spin rate on full shots may rise and a good distance maynot be achieved.

The envelope layer has a total thickness (when there are two envelopelayers, the total thickness of the envelope layer is the sum of theinner envelope layer thickness and the outer envelope layer thickness)which is preferably at least 2.0 mm, more preferably at least 2.7 mm,and even more preferably at least 3.5 mm. The upper limit in thethickness of the envelope layer is preferably not more than 7.0 mm, morepreferably not more than 6.5 mm, and even more preferably not more than6.0 mm. If the total thickness of the envelope layer is too small, thespin rate-lowering effect on full shots with an iron may be inadequateand the intended distance may not be obtained. When the total thicknessof the envelope layer is too large, the initial velocity of the overallball may decline and a good distance is generally not obtained.

The total thickness of the envelope layer preferably satisfies thefollowing condition in the thickness relationship with the subsequentlydescribed intermediate layer and the cover: (coverthickness)<(intermediate layer thickness)≤(total thickness of envelopelayer). Also, the thicknesses of the respective layers have a ratiotherebetween, expressed as (total thickness of envelope layers)/(coverthickness+intermediate layer thickness), whose value is preferably atleast 1.0, more preferably at least 1.5, and even more preferably atleast 1.8; the upper limit is preferably not more than 3.5, morepreferably not more than 3.0, and even more preferably not more than2.6. When this value is too large, the initial velocity may decrease anda good distance may not be obtained, or the durability to cracking onrepeated impact may worsen. On the other hand, when this value is toosmall, the spin rate-lowering effect may be inadequate and a gooddistance may not be achieved.

The inner envelope layer material and outer envelope layer material arenot particularly limited, although known resin materials may be used forthis purpose. The material used in the inner envelope layer and thematerial used in the outer envelope layer may be the same resin or maybe different resins. Of these resin materials, examples of especiallypreferred materials include resin compositions formulated from:

a base resin of (a) an olefin-unsaturated carboxylic acid randomcopolymer and/or a metal ion neutralization product of anolefin-unsaturated carboxylic acid random copolymer blended with (b) anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom terpolymer and/or a metal ion neutralization product of anolefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom terpolymer in a weight ratio between 100:0 and 0:100, and

(c) a Non-Ionomeric Thermoplastic Elastomer

in a weight ratio between 100:0 and 50:50.

The intermediate layer-forming resin material described in, for example,JP-A 2010-253268 may be suitably used as above components (a) to (c).

Depending on the intended use, optional additives may be suitablyincluded in the envelope layer-forming resin material. For example,pigments, dispersants, antioxidants, ultraviolet absorbers and lightstabilizers may be added. When these additives are included, the amountadded per 100 parts by weight of the overall base resin is preferably atleast 0.1 part by weight, and more preferably at least 0.5 part byweight. The upper limit is preferably not more than 10 parts by weight,and more preferably not more than 4 parts by weight.

Next, the intermediate layer is described.

The intermediate layer has a material hardness on the Shore D hardnessscale which, although not particularly limited, is preferably at least58, more preferably at least 60, and even more preferably at least 63.The upper limit is preferably not more than 70, more preferably not morethan 68, and even more preferably not more than 65. The materialhardness on the Shore C hardness scale is preferably at least 87, morepreferably at least 89, and even more preferably at least 93. The upperlimit is preferably not more than 100, more preferably not more than 98,and even more preferably not more than 96.

The sphere obtained by encasing the outer envelope layer-encased spherewith the intermediate layer (intermediate layer-encased sphere) has asurface hardness which, on the Shore D hardness scale, is preferably atleast 64, more preferably at least 66, and even more preferably at least69. The upper limit is preferably not more than 76, more preferably notmore than 74, and even more preferably not more than 71. The surfacehardness on the Shore C hardness scale is preferably at least 90, morepreferably at least 93, and even more preferably at least 96. The upperlimit is preferably not more than 100, more preferably not more than 99,and even more preferably not more than 98.

When the material hardness and surface hardness of the intermediatelayer are lower than the above ranges, the ball may be too receptive tospin on full shots or the initial velocity may become low, as a resultof which a good distance may not be achieved. On the other hand, whenthe material hardness and surface hardness of the intermediate layer arehigher than the above ranges, the durability to cracking on repeatedimpact may worsen or the feel at impact on shots with a putter or onshort approaches may become too hard.

Also, it is desirable for the surface hardness of the intermediatelayer-encased sphere to satisfy the following condition in therelationship with the ball surface hardness:

(Shore C hardness at surface of intermediate layer-encasedsphere)>(Shore C hardness at ball surface).

When this is not the case, the spin rate of the ball on full shots mayrise and a good distance may not be achieved, or the controllability ofthe ball in the short game may worsen.

The intermediate layer has a thickness which is preferably at least 0.7mm, more preferably at least 0.8 mm, and even more preferably at least1.0 mm. The intermediate layer thickness has an upper limit that ispreferably not more than 1.8 mm, more preferably not more than 1.4 mm,and even more preferably not more than 1.2 mm. The intermediate layer ispreferably thicker than the subsequently described cover (outermostlayer). When the intermediate layer has a thickness which falls outsideof the above range or is formed thinner than the cover, the spinrate-lowering effect on shots with a driver (W #1) may be inadequate,which may result in a poor distance. Also, when the intermediate layeris too thin, the durability to cracking on repeated impact and thelow-temperature durability may worsen.

The intermediate layer material may be suitably selected from amongvarious thermoplastic resins that are used as golf ball materials, withthe use of the highly neutralized resin material containing components(a) to (c) described above in connection with the envelope layers or anionomer resin being preferred.

Specific examples of ionomer resin materials include sodium-neutralizedionomer resins and zinc-neutralized ionomer resins. These may be usedsingly or two or more may be used together.

An embodiment that uses in admixture a zinc-neutralized ionomer resinand a sodium-neutralized ionomer resin as the chief material isespecially preferred. The blending ratio therebetween, expressed as theweight ratio (zinc-neutralized ionomer)/(sodium-neutralized ionomer), isfrom 25/75 to 75/25, preferably from 35/65 to 65/35, and more preferablyfrom 45/55 to 55/45. When the zinc-neutralized ionomer andsodium-neutralized ionomer are not included in a ratio within thisrange, the rebound may become too low and the desired distance may notbe achieved, the durability to cracking on repeated impact at normaltemperatures may worsen, or the durability to cracking at lowtemperatures (subzero Centigrade) may worsen.

The resin material used to form the intermediate layer may be oneobtained by blending, of commercially available ionomer resins, ahigh-acid ionomer resin having an acid content of at least 16 wt % withan ordinary ionomer resin. The high rebound and lower spin rateresulting from the use of such a blend enables a good distance to beachieved on driver (W #1) shots.

The amount of unsaturated carboxylic acid included in the high-acidionomer resin (acid content) is generally at least 16 wt %, preferablyat least 17 wt %, and more preferably at least 18 wt %. The upper limitis preferably not more than 22 wt %, more preferably not more than 21 wt%, and even more preferably not more than 20 wt %. When this value istoo small, the spin rate on full shots may rise, as a result of whichthe intended distance may not be attainable. On the other hand, whenthis value is too large, the feel on impact may become too hard, or thedurability to cracking on repeated impact may worsen.

The amount of high-acid ionomer resin included per 100 wt % of the resinmaterial is preferably at least 10 wt %, more preferably at least 30 wt%, and even more preferably at least 60 wt %. When the content of thishigh-acid ionomer resin is too low, the spin rate on shots with a driver(W #1) may rise and a good distance may not be attained.

Depending on the intended use, optional additives may be suitablyincluded in the intermediate layer material. For example, pigments,dispersants, antioxidants, ultraviolet absorbers and light stabilizersmay be added. When these additives are included, the amount added per100 parts by weight of the base resin is preferably at least 0.1 part byweight, and more preferably at least 0.5 part by weight. The upper limitis preferably not more than 10 parts by weight, and more preferably notmore than 4 parts by weight.

It is desirable to abrade the surface of the intermediate layer in orderto increase adhesion of the intermediate layer material with thepolyurethane that is preferably used in the subsequently described covermaterial. In addition, it is desirable to apply a primer (adhesive) tothe surface of the intermediate layer following such abrasion treatmentor to add an adhesion reinforcing agent to the intermediate layermaterial.

The intermediate layer material has a specific gravity which istypically less than 1.1, preferably between 0.90 and 1.05, and morepreferably between 0.93 and 0.99. Outside of this range, the rebound ofthe overall ball may decrease and a good distance may not be obtained,or the durability of the ball to cracking on repeated impact may worsen.

Next, the cover (outermost layer) is described.

The cover has a material hardness on the Shore D hardness scale which,although not particularly limited, is preferably at least 35, morepreferably at least 40, and even more preferably at least 45. The upperlimit is preferably not more than 60, more preferably not more than 55,and even more preferably not more than 50. The material hardness on theShore C hardness scale is preferably at least 57, more preferably atleast 63, and even more preferably at least 70. The upper limit ispreferably not more than 89, more preferably not more than 83, and evenmore preferably not more than 76.

The sphere obtained by encasing the intermediate layer-encased spherewith the cover (i.e. the ball) has a surface hardness on the Shore Dhardness scale that is preferably at least 50, more preferably at least53, and even more preferably at least 56. The upper limit is preferablynot more than 70, more preferably not more than 67, and even morepreferably not more than 64. The material hardness on the Shore Chardness scale is preferably at least 75, more preferably at least 80,and even more preferably at least 85. The upper limit is preferably notmore than 95, more preferably not more than 92, and even more preferablynot more than 90.

When the material hardness of the cover and the ball surface hardnessare lower than the above respective ranges, the spin rate of the ball onfull shots with an iron may rise and a good distance may not beachieved. On the other hand, when the material hardness of the cover andthe ball surface hardness are too high, the ball may not be receptive tospin on approach shots or the scuff resistance may worsen.

The cover has a thickness of preferably at least 0.3 mm, more preferablyat least 0.45 mm, and even more preferably at least 0.6 mm. The upperlimit in the cover thickness is preferably not more than 1.0 mm, morepreferably not more than 0.9 mm, and even more preferably not more than0.85 mm. When the cover is too thick, the rebound on full shots with aniron may become inadequate or the spin rate may rise, as a result ofwhich a good distance may not be achieved. On the other hand, when thecover is too thin, the scuff resistance may worsen or the ball may notbe receptive to spin on approach shots and may thus lack sufficientcontrollability.

Various thermoplastic resins and thermoset resins employed as coverstock in golf balls may be used as the cover material. For reasonshaving to do with controllability and scuff resistance, preferred usecan be made of a urethane resin. In particular, from the standpoint ofthe mass productivity of the manufactured balls, it is preferable to usea material that is composed primarily of a thermoplastic polyurethane,and more preferable to form the cover of a resin blend in which the maincomponents are (I) a thermoplastic polyurethane and (II) apolyisocyanate compound.

It is recommended that the total weight of components (I) and (II)combined be at least 60%, and preferably at least 70%, of the overallamount of the cover-forming resin composition. Components (I) and (II)are described in detail below.

The thermoplastic polyurethane (I) has a structure which includes softsegments composed of a polymeric polyol (polymeric glycol) that is along-chain polyol, and hard segments composed of a chain extender and apolyisocyanate compound. Here, the long-chain polyol serving as astarting material may be any that has hitherto been used in the artrelating to thermoplastic polyurethanes, and is not particularlylimited. Illustrative examples include polyester polyols, polyetherpolyols, polycarbonate polyols, polyester polycarbonate polyols,polyolefin polyols, conjugated diene polymer-based polyols, castoroil-based polyols, silicone-based polyols and vinyl polymer-basedpolyols. These long-chain polyols may be used singly, or two or more maybe used in combination. Of these, in terms of being able to synthesize athermoplastic polyurethane having a high rebound resilience andexcellent low-temperature properties, a polyether polyol is preferred.

Any chain extender that has hitherto been employed in the art relatingto thermoplastic polyurethanes may be suitably used as the chainextender. For example, low-molecular-weight compounds with a molecularweight of 400 or less which have on the molecule two or more activehydrogen atoms capable of reacting with isocyanate groups are preferred.Illustrative, non-limiting, examples of the chain extender include1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanedioland 2,2-dimethyl-1,3-propanediol. Of these, the chain extender ispreferably an aliphatic diol having from 2 to 12 carbon atoms, and ismore preferably 1,4-butylene glycol.

Any polyisocyanate compound hitherto employed in the art relating tothermoplastic polyurethanes may be suitably used without particularlimitation as the polyisocyanate compound. For example, use may be madeof one or more selected from the group consisting of4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluenediisocyanate, p-phenylene diisocyanate, xylylene diisocyanate,1,5-naphthylene diisocyanate, tetramethylxylene diisocyanate,hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate,tetramethylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate, norbomene diisocyanate, trimethylhexamethylenediisocyanate and dimer acid diisocyanate. However, depending on the typeof isocyanate, the crosslinking reactions during injection molding maybe difficult to control. In the practice of the invention, to provide abalance between stability at the time of production and the propertiesthat are manifested, it is most preferable to use the following aromaticdiisocyanate: 4,4′-diphenylmethane diisocyanate.

Commercially available products may be used as the thermoplasticpolyurethane serving as component (I). Illustrative examples includePandex T-8295, Pandex T-8290 and Pandex T-8260 (all from DIC CovestroPolymer, Ltd.).

A thermoplastic elastomer other than the above thermoplasticpolyurethanes may also be optionally included as a separate component,i.e., component (III), together with above components (I) and (II). Byincluding this component (III) in the above resin blend, the flowabilityof the resin blend can be further improved and properties required ofthe golf ball cover material, such as resilience and scuff resistance,can be increased.

The compositional ratio of above components (I), (II) and (III) is notparticularly limited. However, to fully elicit the advantageous effectsof the invention, the compositional ratio (I):(II):(III) is preferablyin the weight ratio range of from 100:2:50 to 100:50:0, and morepreferably from 100:2:50 to 100:30:8.

In addition, various additives other than the ingredients making up theabove thermoplastic polyurethane may be optionally included in thisresin blend. For example, pigments, dispersants, antioxidants, lightstabilizers, ultraviolet absorbers and internal mold lubricants may besuitably included.

The manufacture of multi-piece solid golf balls in which theabove-described core, inner envelope layer, outer envelope layer,intermediate layer and cover (outermost layer) are formed as successivelayers may be carried out by a customary method such as a knowninjection molding process. For example, a multi-piece golf ball can beproduced by successively injection-molding the respective materials forthe inner envelope layer, the outer envelope layer and the intermediatelayer over the core in injection molds for each layer so as to obtainthe respective layer-encased spheres and then, last of all,injection-molding the material for the cover serving as the outermostlayer over the intermediate layer-encased sphere. Alternatively, theencasing layers may each be formed by enclosing the sphere to be encasedwithin two half-cups that have been pre-molded into hemispherical shapesand then molding under applied heat and pressure.

The golf ball has a deflection when compressed under a final load of1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which must be atleast 3.0 mm, and is preferably at least 3.2 mm, and more preferably atleast 3.4 mm. The deflection upper limit value is preferably not morethan 4.5 mm, more preferably not more than 4.2 mm, and even morepreferably not more than 4.0 mm. When the deflection by the golf ball istoo small, i.e., when the ball is too hard, the spin rate risesexcessively so that the ball does not achieve a good distance, or thefeel at impact is too hard. On the other hand, when the deflection istoo large, i.e., when the ball is too soft, the ball rebound may be toolow so that the ball does not achieve a good distance, the feel atimpact may be too soft, or the durability to cracking under repeatedimpact may worsen.

Letting C be the deflection of the core in millimeters when compressedunder a final load of 1,275 N (130 kgf) from an initial load of 98 N (10kgf) and B be the deflection of the ball in millimeters when compressedunder a final load of 1,275 N (130 kgf) from an initial load of 98 N (10kgf), the value of C−B is preferably at least 2.5 mm, more preferably atleast 2.7 mm, and even more preferably at least 2.8 mm; the upper limitvalue is preferably not more than 5.0 mm, more preferably not more than4.6 mm, and even more preferably not more than 4.3 mm. When this valueis too large, the initial velocity on shots may become low and a gooddistance may not be achieved, or the durability to cracking on repeatedimpact may worsen. When this value is too small, the spin rate-loweringeffect may be inadequate and so a good distance may not be achieved.

Hardness Relationships Among Layers

In the invention, it is critical that the Shore C hardness at thesurface of the sphere obtained by encasing the core with the innerenvelope layer (inner envelope layer-encased sphere), the Shore Chardness at the surface of the sphere obtained by encasing the innerenvelope layer-encased sphere with the outer envelope layer (outerenvelope layer-encased sphere), the Shore C hardness at the surface ofthe sphere obtained by encasing the outer envelope layer-encased spherewith the intermediate layer (intermediate layer-encased sphere) and theShore C hardness at the ball surface together satisfy the conditions:

(Shore C hardness at surface of outer envelope layer-encasedsphere)>(Shore C hardness at surface of inner envelope layer-encasedsphere) and

(Shore C hardness at surface of intermediate layer-encasedsphere)>(Shore C hardness at ball surface).

The value obtained by subtracting the surface hardness of the innerenvelope layer-encased sphere from the surface hardness of the outerenvelope layer-encased sphere, expressed on the Shore C hardness scale,is larger than 0, preferably at least 2, and more preferably at least 4.The upper limit value is preferably not more than 15, more preferablynot more than 10, and even more preferably not more than 7. When thesurface hardness of the outer envelope layer-encased sphere is smallerthan the surface hardness of the inner envelope layer-encased sphere,the spin rate of the ball on full shots may rise and the intendeddistance may not be attainable.

The value obtained by subtracting the surface hardness of the ball fromthe surface hardness of the intermediate layer-encased sphere, expressedon the Shore C hardness scale, is larger than 0, preferably at least 3,and more preferably at least 5. The upper limit value is preferably notmore than 30, more preferably not more than 22, and even more preferablynot more than 15. When this value falls outside of the above numericalrange, the spin rate of the ball on full shots may rise and the intendeddistance may not be attainable.

The value obtained by subtracting the surface hardness of the core fromthe surface hardness of the outer envelope layer-encased sphere,expressed on the Shore C hardness scale, is preferably larger than 0,more preferably at least 8, and even more preferably at least 15. Theupper limit value is preferably not more than 50, more preferably notmore than 43, and even more preferably not more than 37. When this valuefalls outside of the above numerical range, the spin rate of the ball onfull shots may rise and the intended distance may not be attainable.

The value obtained by subtracting the core center hardness from thesurface hardness of the outer envelope layer-encased sphere, expressedon the Shore C hardness scale, is preferably at least 29, morepreferably at least 32, and even more preferably at least 35. The upperlimit value is preferably not more than 55, more preferably not morethan 50, and even more preferably not more than 45. When this value istoo large, the durability to cracking on repeated impact may worsen orthe initial velocity on shots may be low, as a result of which theintended distance may not be attainable. On the other hand, when thisvalue is too small, the spin rate on full shots may be high, as a resultof which the intended distance may not be attainable.

In addition, to obtain a spin rate-lowering effect on full shots, it ispreferable for the surface hardness of the intermediate layer-encasedsphere to be higher than the surface hardness of the outer envelopelayer-encased sphere. The value obtained by subtracting the surfacehardness of the outer envelope layer-encased sphere from the surfacehardness of the intermediate layer-encased sphere, expressed on theShore C hardness scale, is preferably greater than 0, more preferably atleast 4, and even more preferably at least 8. The upper limit value ispreferably not more than 28, more preferably not more than 22, and evenmore preferably not more than 16. When this value falls outside of theabove numerical range, the spin rate on full shots may rise, as a resultof which the intended distance may not be attainable.

The value obtained by subtracting the core center hardness from thesurface hardness of the intermediate layer-encased sphere, expressed onthe Shore C hardness scale, is preferably at least 33, more preferablyat least 38, and even more preferably at least 43. The upper limit valueis preferably not more than 65, more preferably not more than 60, andeven more preferably not more than 56. When this value is too large, thedurability to cracking on repeated impact may worsen or the initialvelocity on shots may be low and so the intended distance may not beattainable. On the other hand, when this value is too small, the spinrate on full shots may rise and so the intended distance may not beattainable.

Relationship Between Volume and Hardness of Core and Envelope Layer

Letting Core vh be the product of the core volume (mm³) multiplied bythe Shore C hardness Cm at the midpoint between the core surface and thecore center, IE vh be the product of the volume of the inner envelopelayer (mm³) multiplied by the Shore C hardness at the surface of theinner envelope layer-encased sphere and OE vh be the product of thevolume of the outer envelope layer (mm³) multiplied by the Shore Chardness at the surface of the outer envelope layer-encased sphere, thevalue of (OE vh+IE vh)/Core vh is preferably at least 1.0, morepreferably at least 1.2, and even more preferably at least 1.4. Theupper limit value is preferably not more than 4.5, more preferably notmore than 4.0, and even more preferably not more than 3.5. When thisvalue is too large, the initial velocity on shots may decrease and agood distance may not be achieved, or the durability to cracking onrepeated impact may worsen. On the other hand, when this value is toosmall, the spin rate-lowering effect may be inadequate and so a gooddistance may not be achieved.

Numerous dimples may be formed on the outside surface of the cover(i.e., the outermost layer of the ball). The number of dimples arrangedon the cover surface, although not particularly limited, is preferablyat least 250, more preferably at least 300, and even more preferably atleast 320. The upper limit is preferably not more than 380, morepreferably not more than 350, and even more preferably not more than340. When the number of dimples is higher than this range, the balltrajectory may become lower and the distance traveled by the ball maydecrease. On the other hand, when the number of dimples is lower thatthis range, the ball trajectory may become higher and a good distancemay not be achieved.

The dimple shapes used may be of one type or may be a combination of twoor more types suitably selected from among, for example, circularshapes, various polygonal shapes, dewdrop shapes and oval shapes. Whencircular dimples are used, the dimple diameter may be set to at leastabout 2.5 mm and up to about 6.5 mm, and the dimple depth may be set toat least 0.08 mm and up to 0.30 mm.

In order for the aerodynamic properties to be fully manifested, it isdesirable for the dimple coverage ratio on the spherical surface of thegolf ball, i.e., the dimple surface coverage SR, which is the sum of theindividual dimple surface areas, each defined by the flat planecircumscribed by the edge of a dimple, as a percentage of the sphericalsurface area of the ball were the ball to have no dimples thereon, to beset to at least 70% and not more than 90%. Also, to optimize the balltrajectory, it is desirable for the value Vo, defined as the spatialvolume of the individual dimples below the flat plane circumscribed bythe dimple edge, divided by the volume of the cylinder whose base is theflat plane and whose height is the maximum depth of the dimple from thebase, to be set to at least 0.35 and not more than 0.80. Moreover, it ispreferable for the ratio VR of the sum of the volumes of the individualdimples, each formed below the flat plane circumscribed by the edge of adimple, with respect to the volume of the ball sphere were the ballsurface to have no dimples thereon, to be set to at least 0.6% and notmore than 1.0%. Outside of the above ranges in these respective values,the resulting trajectory may not enable a good distance to be achievedand so the ball may fail to travel a fully satisfactory distance.

A coating layer may be formed on the surface of the cover. This coatinglayer can be formed by applying various types of coating materials.Because the coating layer must be capable of enduring the harshconditions of golf ball use, it is desirable to use a coatingcomposition in which the chief component is a urethane coating materialcomposed of a polyol and a polyisocyanate.

The polyol component is exemplified by acrylic polyols and polyesterpolyols. These polyols include modified polyols. To further increaseworkability, other polyols may also be added.

It is suitable to use two types of polyester polyols together as thepolyol component. In this case, letting the two types of polyesterpolyol be component (a) and component (b), a polyester polyol in which acyclic structure has been introduced onto the resin skeleton may be usedas the polyester polyol of component (a). Examples include polyesterpolyols obtained by the polycondensation of a polyol having an alicyclicstructure, such as cyclohexane dimethanol, with a polybasic acid; andpolyester polyols obtained by the polycondensation of a polyol having analicyclic structure with a diol or triol and a polybasic acid. Apolyester polyol having a branched structure may be used as thepolyester polyol of component (b). Examples include polyester polyolshaving a branched structure, such as NIPPOLAN 800, from TosohCorporation.

The polyisocyanate is exemplified without particular limitation bycommonly used aromatic, aliphatic, alicyclic and other polyisocyanates.Specific examples include tolylene diisocyanate, diphenylmethanediisocyanate, xylylene diisocyanate, tetramethylene diisocyanate,hexamethylene diisocyanate, lysine diisocyanate, isophoronediisocyanate, 1,4-cyclohexylene diisocyanate, naphthalene diisocyanate,trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanateand 1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane. Thesemay be used singly or in admixture.

Depending on the coating conditions, various types of organic solventsmay be mixed into the coating composition. Examples of such organicsolvents include aromatic solvents such as toluene, xylene andethylbenzene; ester solvents such as ethyl acetate, butyl acetate,propylene glycol methyl ether acetate and propylene glycol methyl etherpropionate; ketone solvents such as acetone, methyl ethyl ketone, methylisobutyl ketone and cyclohexanone; ether solvents such as diethyleneglycol dimethyl ether, diethylene glycol diethyl ether and dipropyleneglycol dimethyl ether; alicyclic hydrocarbon solvents such ascyclohexane, methyl cyclohexane and ethyl cyclohexane; and petroleumhydrocarbon solvents such as mineral spirits.

The thickness of the coating layer made of the coating composition,although not particularly limited, is typically from 5 to 40 μm, andpreferably from 10 to 20 μm. As used herein, “coating layer thickness”refers to the coating thickness obtained by averaging the measurementstaken at a total of three places: the center of a dimple and two placeslocated at positions between the dimple center and the dimple edge.

In this invention, the coating layer composed of the above coatingcomposition has an elastic work recovery that is preferably at least60%, and more preferably at least 80%. At a coating layer elastic workrecovery in this range, the coating layer has a high elasticity and sothe self-repairing ability is high, resulting in an outstanding abrasionresistance. Moreover, the performance attributes of golf balls coatedwith this coating composition can be improved. The method of measuringthe elastic work recovery is described below.

The elastic work recovery is one parameter of the nanoindentation methodfor evaluating the physical properties of coating layers, this being ananohardness test method that controls the indentation load on amicro-newton (μN) order and tracks the indenter depth during indentationto a nanometer (nm) precision. In prior methods, only the size of thedeformation (plastic deformation) mark corresponding to the maximum loadcould be measured. However, in the nanoindentation method, therelationship between the indentation load and the indentation depth canbe obtained by continuous automated measurement. Hence, unlike in thepast, there are no individual differences between observers whenvisually measuring a deformation mark under an optical microscope, andso it is thought that the physical properties of the coating layer canbe precisely evaluated. Given that the coating layer on the ball surfaceis strongly affected by the impact of drivers and other clubs and has anot inconsiderable influence on various golf ball properties, measuringthe coating layer by the nanohardness test method and carrying out suchmeasurement to a higher precision than in the past is a very effectivemethod of evaluation.

The hardness of the coating layer, as expressed on the Shore M hardnessscale, is preferably at least 40, and more preferably at least 60. Theupper limit is preferably not more than 95, and more preferably not morethan 85. This Shore M hardness is obtained in accordance with ASTMD2240. The hardness of the coating layer, as expressed on the Shore Chardness scale, is preferably at least 40, and more preferably at least50; the upper limit is preferably not more than 80, and more preferablynot more than 70. This Shore C hardness is obtained in accordance withASTM D2240. At coating layer hardnesses that are higher than theseranges, the coating may become brittle when the ball is repeatedlystruck, which may make it incapable of protecting the cover layer. Onthe other hand, coating layer hardnesses that are lower than the aboverange are undesirable because the ball surface is more easily damagedwhen striking a hard object.

When the above coating composition is used, the formation of a coatinglayer on the surface of golf balls manufactured by a commonly knownmethod can be carried out via the steps of preparing the coatingcomposition at the time of application, applying the composition ontothe golf ball surface by a conventional coating operation, and dryingthe applied composition. The coating method is not particularly limited.For example, spray painting, electrostatic painting or dipping may besuitably used.

The multi-piece solid golf ball of the invention can be made to conformto the Rules of Golf for play. The inventive ball may be formed to adiameter which is such that the ball does not pass through a ring havingan inner diameter of 42.672 mm, and to a weight which is preferablybetween 45.0 and 45.93 g.

The golf ball has an initial velocity, based on The Royal and AncientGolf Club of St. Andrews (R&A) Rules of Golf, which is generally atleast 76.8 m/s, preferably at least 77.0 m/s, and more preferably atleast 77.1 m/s, and which has an upper limit of not more than 77.724m/s. When this initial velocity exceeds 77.724 m/s, it falls outside ofthe official rules. On the other hand, when the initial velocity is toolow, a good distance may not be achieved on full shots.

EXAMPLES

The following Examples and Comparative Examples are provided toillustrate the invention, and are not intended to limit the scopethereof.

Examples 1 to 4, Comparative Examples 1 to 8

Solid cores were produced by preparing rubber compositions for theExamples and Comparative Examples shown in Table 1, and then molding andvulcanizing the compositions under the vulcanization conditions for eachExample shown in Table 1.

In Examples 3 and 4 and Comparative Examples 7 and 8, the core isproduced in the same way as above based on the formulation shown inTable 1.

TABLE 1 Example Comparative Example 1 2 3 4 1 2 3 4 5 6 7 8 CorePolybutadiene 100 100 100 100 100 100 100 100 100 100 100 100formulation Zinc acrylate 12.0 7.0 13.0 18.0 8.0 13.0 18.0 32.5 33.232.0 18.0 18.0 (pbw) Organic peroxide 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.21.2 1.2 1.2 1.2 Zinc stearate 5 5 5 5 5 5 5 0 0 0 5 5 Antioxidant 0.10.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 98.0 98.7 61.859.0 60.0 63.3 62.5 29.2 28.9 29.3 59.0 63.6 Zinc salt of 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 pentachlorothiophenol VulcanizationTemperature (° C.) 155 155 155 155 155 155 155 155 155 155 155 155 Time(minutes) 16 16 16 16 20 15 15 15 15 15 16 15

Details on the ingredients mentioned in Table 1 are given below.

-   Polybutadiene: Available under the trade name “BR 730” from JSR    Corporation-   Zinc acrylate: “ZN-DA85S” from Nippon Shokubai Co., Ltd.-   Organic Peroxide: A mixture of 1,1-di(t-butylperoxy)cyclohexane and    silica, available under the trade name “Perhexa C-40” from NOF    Corporation-   Zinc stearate: Available under the trade name “Zinc Stearate G” from    NOF Corporation-   Antioxidant: 2,2′-Methylenebis(4-methyl-6-butylphenol), available    under the trade name “Nocrac NS-6” from Ouchi Shinko Chemical    Industry Co., Ltd.-   Zinc oxide: Available as Grade 3 Zinc Oxide from Sakai Chemical Co.,    Ltd.-   to Zinc salt of pentachlorothiophenol: Available from Wako Pure    Chemical Industries, Ltd.

Formation of Inner and Outer Envelope Layers

Next, in the Examples and the Comparative Examples other thanComparative Examples 4 to 6, an inner envelope layer was formed byinjection-molding the inner envelope layer material of formulation No. 1shown in Table 2 over the core. An outer envelope layer was then formedby injection-molding the outer envelope layer material of formulationNo. 1, No. 2 or No. 3 shown in the same table over the inner envelopelayer. In Comparative Examples 4 to 6, a single envelope layer (detailsfor which are shown in the “Outer envelope layer” section of Table 5)was formed by injection molding the material of formulation No. 1 or No.3 in Table 2 over the core.

In Examples 3 and 4 and Comparative Examples 7 and 8, the envelopelayers are produced in the same way as above based on the formulationsshown in Table 2.

Formation of Intermediate Layer and Cover (Outermost Layer)

Next, in all of the Examples and Comparative Examples, an intermediatelayer was formed by injection molding the intermediate layer material offormulation No. 4 or No. 5 shown in Table 2 over the envelopelayer-encased sphere obtained as described above. A cover (outermostlayer) was then formed by injection-molding the cover material offormulation No. 6 or No. 7 shown in Table 2 over the intermediatelayer-encased sphere in each Example. A plurality of given dimplescommon to all of the Examples and Comparative Examples were formed atthis time on the surface of the cover.

In Examples 3 and 4 and Comparative Examples 7 and 8, the intermediatelayer and the cover are produced in the same way as above based on theformulations shown in Table 2.

TABLE 2 Resin material (pbw) No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7HPF 1000 100 64 HPF 2000 100 Himilan 1605 50 36 Himilan 1557 15 Himilan1706 35 Surlyn 8120 75 Dynaron 6100P 25 Behenic acid 20 Calciumhydroxide 2.3 Calcium stearate 0.15 Zinc stearate 0.15Trimethylolpropane 1.1 1.1 TPU (1) 100 TPU (2) 100

Trade names of the chief materials mentioned in the table are givenbelow.

-   HPF 1000, HPF 2000: HPF™ from The Dow Chemical Company-   Himilan 1605, Himilan 1557, Himilan 1706:    -   Ionomers available from Dow-Mitsui Polychemicals Co., Ltd.-   Surlyn 8120: An ionomer available from The Dow Chemical Company-   Dynaron 6100P: A hydrogenated polymer available from JSR Corporation-   Behenic acid: NAA222-S(beads) from NOF Corporation-   Calcium hydroxide: Available as “CLS-B” from Shiraishi Calcium    Kaisha, Ltd.-   Trimethylolpropane: Available from Tokyo Chemical Industry Co., Ltd.-   TPU (1), TPU (2): Ether-type thermoplastic polyurethanes available    under the trade name “Pandex” from DIC Covestro Polymer, Ltd.

Eight types of circular dimples are used. The dimples and the dimplepattern are common to all of the Examples and Comparative Examples.Details on the dimples are shown in Table 3 below, and the dimplepattern is shown in FIG. 2. FIG. 2A is a top view of the dimples, andFIG. 2B is a side view of the same.

TABLE 3 Cylinder Diameter Depth Volume volume SR VR Dimple A Number (mm)(mm) (mm³) ratio (%) (%) A-1 12 4.6 0.118 1.111 0.566 82.3 0.77 A-2 1984.45 0.117 1.031 0.566 A-3 36 3.85 0.114 0.752 0.566 A-4 12 2.75 0.0850.286 0.566 A-5 36 4.45 0.126 1.110 0.566 A-6 24 3.85 0.123 0.811 0.566A-7 6 3.4 0.115 0.558 0.534 A-8 6 3.3 0.115 0.526 0.534 Total 330

Dimple Definitions

-   Edge: Highest place in cross-section passing through center of    dimple.-   Diameter: Diameter of flat plane circumscribed by edge of dimple.-   Depth: Maximum depth of dimple from flat plane circumscribed by edge    of dimple.-   SR: Sum of individual dimple surface areas, each defined by flat    plane circumscribed by edge of dimple, as a percentage of spherical    surface area of ball were it to have no dimples thereon.-   Dimple volume: Dimple volume below flat plane circumscribed by edge    of dimple.-   Cylinder volume ratio:    -   Ratio of dimple volume to volume of cylinder having same        diameter and depth as dimple.-   VR: Sum of volumes of individual dimples formed below flat plane    circumscribed by edge of dimple, as a percentage of volume of ball    sphere were it to have no dimples thereon.

Formation of Coating Layer

Next, using the coating composition shown in Table 4 below, a coatingcomposition common to all the Examples and Comparative Examples wasapplied with an air spray gun onto the surface of the cover (outermostlayer) on which numerous dimples were formed, thereby producing golfballs having a 15 μm-thick coating layer formed thereon.

The above coating is similarly applied in Examples 3 and 4 andComparative Examples 7 and 8, thereby producing golf balls having a 15μm-thick coating layer formed thereon.

TABLE 4 Coating Base resin Polyester polyol (A) 23 Composition CPolyester polyol (B) 15 (pbw) Organic solvent 62 Curing agent Isocyanate(HMDI isocyanurate) 42 Solvent 58 Molar blending ratio (NCO/OH) 0.89Coating Elastic work recovery (%) 84 properties Shore M hardness 84Shore C hardness 63 Thickness (μm) 15

Polyester Polyol (A) Synthesis Example

A reactor equipped with a reflux condenser, a dropping funnel, a gasinlet and a thermometer was charged with 140 parts by weight oftrimethylolpropane, 95 parts by weight of ethylene glycol, 157 parts byweight of adipic acid and 58 parts by weight of1,4-cyclohexanedimethanol, following which the temperature was raised tobetween 200° C. and 240° C. under stirring and the reaction was effectedby 5 hours of heating. This yielded Polyester Polyol (A) having an acidvalue of 4, a hydroxyl value of 170 and a weight-average molecularweight (Mw) of 28,000.

The Polyester Polyol (A) thus synthesized was then dissolved in butylacetate, thereby preparing a varnish having a nonvolatiles content of 70wt %.

The base resin for Coating Composition C in Table 4 was prepared bymixing together 23 parts by weight of the above polyester polyolsolution, 15 parts by weight of Polyester Polyol (B) (the saturatedaliphatic polyester polyol NIPPOLAN 800 from Tosoh Corporation;weight-average molecular weight (Mw), 1,000; 100% solids) and theorganic solvent. This mixture had a nonvolatiles content of 38.0 wt %.

Elastic Work Recovery

The elastic work recovery of the coating material is measured using acoating sheet having a thickness of 50 μm. The ENT-2100 nanohardnesstester from Erionix Inc. is used as the measurement apparatus, and themeasurement conditions are as follows.

-   -   Indenter: Berkovich indenter (material: diamond; angle α:        65.03°)    -   Load F: 0.2 mN    -   Loading time: 10 seconds    -   Holding time: 1 second    -   Unloading time: 10 seconds

The elastic work recovery is calculated as follows, based on theindentation work W_(elast) (Nm) due to spring-back deformation of thecoating and on the mechanical indentation work W_(total) (Nm).

Elastic work recovery=W _(elast) /W _(total)×100(%)

Shore C Hardness and Shore M Hardness

The Shore C hardness and Shore M hardness in Table 4 above weredetermined by forming the material being tested into 2 mm thick sheetsand stacking three such sheets together to give test specimens.Measurements were taken using a Shore C durometer and a Shore Mdurometer in accordance with ASTM D2240.

Various properties of the resulting golf balls, including the internalhardness of the core, the diameters of the core and each layer-encasedsphere, the thickness and material hardness of each layer, and thesurface hardness of each layer-encased sphere, were evaluated by thefollowing methods. The results are presented in Tables 5 and 6.

Diameters of Core, Inner and Outer Envelope Layer-Encased Spheres andIntermediate Layer-Encased Sphere

The diameters at five random places on the surface were measured at atemperature of 23.9±1° C. and, using the average of these measurementsas the measured value for a single core, inner envelope layer-encasedsphere, outer envelope layer-encased sphere or intermediatelayer-encased sphere, the average diameter for ten such spheres wasdetermined.

Ball Diameter

The diameter at 15 random dimple-free areas was measured at atemperature of 23.9±1° C. and, using the average of these measurementsas the measured value for a single ball, the average diameter for tenballs was determined.

Deflections of Core, Various Layer-Encased Spheres and Ball

The sphere to be measured, be it a core, any of the variouslayer-encased spheres or a ball, was placed on a hard plate and theamount of deflection when compressed under a final load of 1,275 N (130kgf) from an initial load of 98 N (10 kgf) was measured. The amount ofdeflection refers in each case to the measured value obtained afterholding the sphere to be measured isothermally at 23.9° C. The rate atwhich pressure is applied by the head was set to 10 mm/s.

Core Hardness Profile

The indenter of a durometer was set substantially perpendicular to thespherical surface of the core, and the core surface hardness on theShore C hardness scale was measured in accordance with ASTM D2240. TheP2 Automatic Rubber Hardness Tester (Kobunshi Keiki Co., Ltd.) equippedwith a Shore C durometer can be used for measuring the hardness. Themaximum value was read off as the hardness value. Measurements were allcarried out in a 23±2° C. environment. Cross-sectional hardnesses atspecific positions in each core, these hardnesses being the core centerhardness Cc, the core surface hardness Cs and the hardness Cm at themidpoint between the core center and surface, were measured byperpendicularly pressing the indenter of a durometer at the place to bemeasured on the flat cross-section obtained by cutting the core intohemispheres. The results are indicated as Shore C hardness values.

Material Hardnesses (Shore C and D Hardnesses) of Inner and OuterEnvelope Layers, Intermediate Layer and Cover

The resin material for each layer was molded into a sheet having athickness of 2 mm and left to stand for at least two weeks at 23±2° C.Three such sheets were stacked together at the time of measurement. TheShore C hardness and Shore D hardness of each material were measuredwith, respectively, a Shore C durometer and a Shore D durometer inaccordance with ASTM D2240. The P2 Automatic Rubber Hardness Tester(Kobunshi Keiki Co., Ltd.) on which a Shore C durometer or a Shore Ddurometer has been mounted was used for measuring the hardness. Themaximum value was read off as the hardness value.

Surface Hardnesses (Shore C and Shore D) of Inner and Outer EnvelopeLayer-Encased Spheres, Intermediate Layer-Encased Sphere and Ball

These hardnesses were measured by perpendicularly pressing an indenteragainst the surfaces of the respective spheres. The surface hardness ofa ball (cover) is the value measured at a dimple-free area (land) on thesurface of the ball. The Shore C hardness and Shore D hardness in eachcase were measured with, respectively, a Shore C durometer and a Shore Ddurometer in accordance with ASTM D2240. The P2 Automatic RubberHardness Tester (Kobunshi Keiki Co., Ltd.) on which a Shore C durometeror a Shore D durometer has been mounted was used for measuring thehardness. The maximum value was read off as the hardness value.

Ball Initial Velocity

The initial velocity of the ball was measured using an initial velocitymeasuring apparatus of the same type as the USGA drum rotation-typeinitial velocity instrument approved by the R&A. The ball was tested ina chamber at a room temperature of 23±2° C. after being heldisothermally at a temperature of 23±1° C. for at least 3 hours. Onedozen balls were each hit four times using a 250-pound (113.4 kg) head(striking mass) at an impact velocity of 143.8 ft/s (43.83 m/s), and thetime taken for the balls to traverse a distance of 6.28 ft (1.91 m) wasmeasured and used to compute the initial velocity (m/s). This cycle wascarried out over a period of about 15 minutes.

TABLE 5 Example Comparative Example 1 2 3 4 1 2 Construction 5-piece5-piece 5-piece 5-piece 5-piece 5-piece Core Diameter (mm) 26.77 26.7330.71 30.83 30.30 30.23 Weight (g) 15.8 15.7 20.8 20.9 20.2 20.0 Volume(mm³) 10.0 10.0 15.2 15.3 14.6 14.5 Deflection (mm) 6.8 8.0 7.5 6.3 8.87.5 Shore C hardness at surface (Cs) 60.7 50.9 56.4 65.3 46.1 56.4 ShoreC hardness at midpoint 50.5 43.1 47.8 58.6 39.2 47.7 between surface andcenter (Cm) Shore C hardness at center (Cc) 48.4 42.0 43.8 53.3 38.643.8 Shore C hardness difference 12.3 12.6 12.6 12.0 7.5 12.6 betweensurface and center (Cs − Cm)/(Cm − Cc) 4.7 2.1 2.1 1.3 12.6 2.2 Corevolume × Hardness at midpoint 507 431 725 899 570 690 between coresurface and center (Core vh) Inner envelope layer Material No. 1 No. 1No. 1 No. 1 No. 1 No. 1 Thickness (mm) 2.88 2.88 2.25 2.20 2.20 2.25Volume (mm³) 8.0 8.0 7.7 7.5 7.3 7.5 Material hardness (Shore C) 72 7272 72 72 72 Material hardness (Shore D) 47 47 47 47 47 47 Inner envelopeDiameter (mm) 32.52 32.49 35.20 35.23 34.70 34.73 layer-encased Weight(g) 23.4 23.3 28.1 28.1 27.1 27.1 sphere Deflection (mm) 6.0 7.0 6.8 5.77.9 6.8 Surface hardness (Shore C) 83.1 82.5 82.0 82.2 82.2 82.2 Shorehardness (Shore D) 54.4 54.3 54.3 54.5 54.5 54.5 Inner envelope layersurface hardness − 22.5 31.6 25.6 16.8 36.1 25.8 Core surface hardness(Shore C) Inner envelope layer volume × 662 657 630 620 601 614 Shore Csurface hardness of inner envelope layer-encased sphere (IE vh) Outerenvelope layer Material No. 2 No. 2 No. 2 No. 2 No. 1 No. 1 Thickness(mm) 2.85 2.87 1.79 1.77 1.81 1.79 Volume (mm³) 11.2 11.3 7.7 7.6 7.67.5 Material hardness (Shore C) 82 82 82 82 72 72 Material hardness(Shore D) 51 51 51 51 47 47 Total thickness of envelope layer (mm) 5.75.7 4.0 4.0 4.0 4.0 Outer envelope Diameter (mm) 38.22 38.23 38.78 38.7738.32 38.32 layer-encased Weight (g) 34.0 34.0 35.4 35.4 34.3 34.3sphere Deflection (mm) 4.6 5.1 5.8 4.9 6.8 5.9 Surface hardness (ShoreC) 88.3 88.3 88.5 88.0 82.2 82.2 Surface hardness (Shore D) 59 59 59 5954 54 Outer envelope layer surface hardness − 40 46 45 35 44 38 Corecenter hardness (Shore C) Outer envelope layer surface hardness − 28 3732 23 36 26 Core surface hardness (Shore D) Outer envelope layer surfacehardness − 5 6 6 6 0 0 Inner envelope layer surface hardness (Shore C)Outer envelope layer volume × 991 998 681 671 623 618 Surface hardnessof outer envelope layer-encased sphere (OE vh) Comparative Example 3 4 56 7 8 Construction 5-piece 4-piece 4-piece 4-piece 5-piece 5-piece CoreDiameter (mm) 30.36 35.06 35.07 35.04 30.83 29.63 Weight (g) 20.3 27.727.6 27.8 20.9 18.9 Volume (mm³) 14.6 22.6 22.6 22.5 15.3 13.6Deflection (mm) 6.3 3.5 3.3 3.6 6.3 6.3 Shore C hardness at surface (Cs)65.3 82.9 82.9 80.2 65.3 65.3 Shore C hardness at midpoint 57.3 72.972.4 73.6 58.6 58.6 between surface and center (Cm) Shore C hardness atcenter (Cc) 53.3 63.6 64.0 64.4 53.3 53.3 Shore C hardness difference12.0 19.3 18.9 15.8 12.0 12.0 between surface and center (Cs − Cm)/(Cm −Cc) 2.0 1.1 1.2 0.7 1.3 1.3 Core volume × Hardness at midpoint 839 16451636 1658 899 798 between core surface and center (Core vh) Innerenvelope layer Material No. 1 No. 1 No. 1 Thickness (mm) 2.20 2.20 2.20Volume (mm³) 7.3 7.5 7.0 Material hardness (Shore C) 72 72 72 Materialhardness (Shore D) 47 47 47 Inner envelope Diameter (mm) 34.75 35.2334.03 layer-encased Weight (g) 27.2 28.1 25.6 sphere Deflection (mm) 5.75.7 5.7 Surface hardness (Shore C) 82.2 82.2 82.2 Shore hardness (ShoreD) 54.5 54.5 54.5 Inner envelope layer surface hardness − 16.8 16.8 16.8Core surface hardness (Shore C) Inner envelope layer volume × 602 620576 Shore C surface hardness of inner envelope layer-encased sphere (IEvh) Outer envelope layer Material No. 1 No. 3 No. 1 No. 3 No. 2 No. 2Thickness (mm) 1.78 1.63 1.64 1.62 1.77 1.77 Volume (mm³) 7.5 6.9 7.06.8 7.6 7.1 Material hardness (Shore C) 72 80 82 80 82 82 Materialhardness (Shore D) 47 50 51 50 51 51 Total thickness of envelope layer(mm) 4.0 1.6 1.6 1.6 4.0 4.0 Outer envelope Diameter (mm) 38.32 38.3238.36 38.28 38.77 37.57 layer-encased Weight (g) 34.4 34.2 34.2 34.235.4 32.4 sphere Deflection (mm) 5.1 3.2 3.2 3.4 4.9 4.9 Surfacehardness (Shore C) 82.2 85.9 82.9 85.9 88.0 88.0 Surface hardness (ShoreD) 54 57 55 57 59 59 Outer envelope layer surface hardness − 29 22 19 2235 35 Core center hardness (Shore C) Outer envelope layer surfacehardness − 17 3 0 6 23 23 Core surface hardness (Shore D) Outer envelopelayer surface hardness − 0 — — — 6 6 Inner envelope layer surfacehardness (Shore C) Outer envelope layer volume × 616 593 578 588 671 671Surface hardness of outer envelope layer-encased sphere (OE vh)

TABLE 6 Example Comparative Example 1 2 3 4 1 2 Intermediate layerMaterial No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 Thickness (mm) 1.21 1.221.16 1.16 1.16 1.18 Material hardness (Shore C) 95 95 95 95 95 95Material hardness (Shore D) 64 64 64 64 64 64 Intermediate Diameter (mm)40.64 40.67 41.10 41.10 40.64 40.69 layer-encased Weight (g) 39.7 39.740.9 40.9 39.8 39.8 sphere Deflection (mm) 3.5 3.7 4.3 3.8 4.8 4.4Surface hardness (Shore C) 98 98 98 98 98 98 Surface hardness (Shore D)70 70 70 70 70 70 Intermediate layer surface hardness − 9 9 9 10 15 15Outer envelope layer surface hardness (Shore C) Intermediate layersurface hardness − 49 56 54 44 59 54 Core center hardness (Shore C)Cover Material No. 6 No. 6 No. 6 No. 6 No. 6 No. 6 Thickness (mm) 1.000.99 0.80 0.80 1.00 0.99 Material hardness (Shore C) 76 76 76 76 76 76Material hardness (Shore D) 50 50 50 50 50 50 Coating Material C C C C CC layer Material hardness (Shore C) 63 63 63 63 63 63 Ball Diameter (mm)42.65 42.65 42.70 42.70 42.65 42.67 Weight (g) 45.4 45.3 45.5 45.5 45.545.3 Deflection (mm) 3.1 3.3 3.8 3.4 4.2 3.9 Initial velocity (m/s) 77.477.4 77.3 77.5 76.8 77.1 Surface hardness (Shore C) 87 87 89 89 87 87Surface hardness (Shore D) 61 61 62 62 61 61 Total thickness of envelopelayer/(Cover 2.6 2.6 2.1 2.0 1.8 1.9 thickness + Intermediate layerthickness) Core diameter/Ball diameter 0.628 0.627 0.719 0.722 0.7110.709 Intermediate layer surface hardness − 11 11 9 9 11 11 Ball surfacehardness (Shore C) Core deflection − Ball deflection (mm) 3.6 4.7 3.82.8 4.6 3.6 (OE vh + IE vh)/Core vh 3.3 3.8 1.8 1.4 2.1 1.8 ComparativeExample 3 4 5 6 7 8 Intermediate layer Material No. 4 No. 4 No. 4 No. 4No. 5 No. 4 Thickness (mm) 1.17 1.21 1.16 1.18 1.16 1.16 Materialhardness (Shore C) 95 95 95 95 84 95 Material hardness (Shore D) 64 6464 64 56 64 Intermediate Diameter (mm) 40.67 40.74 40.68 40.64 41.1039.90 layer-encased Weight (g) 39.8 39.7 39.6 39.7 40.9 37.6 sphereDeflection (mm) 4.0 2.7 2.9 2.9 3.9 3.8 Surface hardness (Shore C) 98 9898 98 92 98 Surface hardness (Shore D) 70 70 70 70 62 70 Intermediatelayer surface hardness − 15 12 15 12 4 10 Outer envelope layer surfacehardness (Shore C) Intermediate layer surface hardness − 44 34 34 33 3944 Core center hardness (Shore C) Cover Material No. 6 No. 6 No. 6 No. 6No. 7 No. 6 Thickness (mm) 1.00 0.98 1.00 1.00 0.80 1.40 Materialhardness (Shore C) 76 76 76 76 86 76 Material hardness (Shore D) 50 5050 50 57 50 Coating Material C C C C C C layer Material hardness (ShoreC) 63 63 63 63 63 63 Ball Diameter (mm) 42.67 42.70 42.68 42.65 42.7042.70 Weight (g) 45.5 45.3 45.3 45.4 45.5 45.5 Deflection (mm) 3.6 2.62.7 2.7 3.4 3.2 Initial velocity (m/s) 77.2 77.2 77.6 77.2 76.8 76.9Surface hardness (Shore C) 87 87 87 87 94 86 Surface hardness (Shore D)61 61 61 61 64 57 Total thickness of envelope layer/(Cover 1.8 0.7 0.80.7 2.0 1.5 thickness + Intermediate layer thickness) Core diameter/Balldiameter 0.711 0.821 0.822 0.822 0.722 0.694 Intermediate layer surfacehardness − 11 11 11 11 −2 12 Ball surface hardness (Shore C) Coredeflection − Ball deflection (mm) 2.6 0.9 0.6 0.9 2.9 3.1 (OE vh + IEvh)/Core vh 1.5 0.4 0.4 0.4 1.4 1.6

The flight performance (W #1, I #6), spin rate on approach shots, feelat impact and durability on repeated impact of each golf ball wereevaluated by the following methods. The results are shown in Table 7.

Flight Performance (W #1)

A driver (W #1) was mounted on a golf swing robot and the distancetraveled by the ball when struck at a head speed of 45 m/s was measuredand rated according to the criteria shown below. The club used was theTourB XD-5 (W #1; loft angle, 9.5°) manufactured by Bridgestone SportsCo., Ltd. In addition, using an apparatus for measuring the initial toconditions, the spin rate was measured immediately after the ball wassimilarly struck.

Rating Criteria

Good: Total distance was 235.0 m or more

NG: Total distance was less than 235.0 m

Flight Performance (I #6)

A number six iron (I #6) was mounted on a golf swing robot and thedistance traveled by the ball when struck at a head speed of 44 m/s wasmeasured and rated according to the criteria shown below. The club usedwas the TourB X-CB (I #6) manufactured by Bridgestone Sports Co., Ltd.In addition, using an apparatus for measuring the initial conditions,the spin rate was measured immediately after the ball was similarlystruck.

Rating Criteria

Good: Total distance was 180.0 m or more

NG: Total distance was less than 180.0 m

Evaluation of Spin Rate on Approach Shots

A sand wedge (SW) was mounted on a golf swing robot and the amount ofspin by the ball when struck at a head speed of 20 m/s was ratedaccording to the criteria shown below. An apparatus for measuring theinitial conditions was used to measure the spin rate immediately afterthe ball was struck. The sand wedge was the TourB XW-1 (SW) manufacturedby Bridgestone Sports Co., Ltd.

Rating Criteria:

Good: Spin rate was 5,900 rpm or more

NG: Spin rate was less than 5,900 rpm

Feel

The feel of the ball when struck on full shots with a driver (W #1) andan iron (I #6) by amateur golfers having a handicap of 15 to 25 wasrated according to the criteria shown below.

Rating Criteria:

-   -   Good: Fifteen or more out of 20 golfers rated the ball as having        a very soft and good feel    -   Fair: At least 10 and up to 14 out of 20 golfers rated the ball        as having a soft and good feel

Durability to Cracking on Repeated Impact

A driver (W #1) was mounted on a golf swing robot, N=10 sample ballswere repeatedly struck at a head speed of 45 m/s, and the durability ofthe balls was evaluated according to the criteria shown below.

Evaluation Criteria:

Using ten balls, the number of shots required for each ball to begincracking was counted. Of the ten balls, the three balls having thelowest number of shots were selected, and the average number of shotsfor these three balls was treated as the “number of shots required forcracking.” Durability indices for the balls in the respective Exampleswere calculated relative to an arbitrary value of 100 for the number ofshots required for the ball in Example 2 to crack.

Good: Index was 90 or more

NG: Index was less than 90

TABLE 7 Example Comparative Example 1 2 3 4 1 2 3 4 5 6 7 8 Flight W#1Spin 2,336 2,317 2,251 2,294 2,334 2,357 2,380 2,725 2,645 2,706 2,3452,419 HS: 45 rate m/s (rpm) Total 240.1 235.4 235.7 236.7 232.0 234.0235.5 238.2 238.7 237.1 235.1 233.1 distance (m) Rating good good goodgood NG NG good good good good good NG Flight I#6 Spin 5,539 5,455 5,2065,351 5,125 5,061 5,334 6,533 6,546 6,363 5,591 5,521 HS: 44 rate m/s(rpm) Total 182.5 180.1 183.3 181.8 180.2 182.6 179.5 173.6 176.9 175.9179.8 180.5 distance (m) Rating good good good good good good NG NG NGNG NG good Approach HS: Spin 6,364 6,179 5,921 5,973 6,044 5,996 6,1166,381 6,386 6,361 5,721 6,173 shots 20 rate m/s (rpm) Rating good goodgood good good good good good good good NG good Feel at impact Ratinggood good good good good good good NG NG NG good good Durability toRating good good good good NG good good good good good good goodrepeated impact

As demonstrated by the results in Table 7, the golf balls of ComparativeExamples 1 to 8 are inferior in the following respects to the golf ballsaccording to the present invention obtained in Examples 1 to 4.

In Comparative Example 1, the surface hardness of the outer envelopelayer is higher than the surface hardness of the inner envelope layer.As a result, the spin rate on shots with a driver (W #1) rises and theinitial velocity of the ball when struck decreases, and so a gooddistance is not obtained. In addition, the durability to cracking onrepeated impact is low.

In Comparative Example 2, the surface hardness of the outer envelopelayer is higher than the surface hardness of the inner envelope layer.As a result, the spin rate on shots with a driver (W #1) rises and theinitial velocity of the ball when struck decreases, and so a gooddistance is not obtained. In addition, the durability to cracking onrepeated impact is low.

In Comparative Example 3, the surface hardness of the outer envelopelayer is higher than the surface hardness of the inner envelope layer.As a result, the spin rate on shots with an iron (I #6) rises and theinitial velocity of the ball when struck decreases, and so a gooddistance is not obtained.

In Comparative Example 4, the ball deflection is less than 3.0 mm andthe ball has a four-layer construction. As a result, the spin rate onshots with an iron (I #6) rises and a good distance is not obtained.

In Comparative Example 5, the ball deflection is less than 3.0 mm andthe ball has a four-layer construction. As a result, the spin rate onshots with an iron (I #6) rises and a to good distance is not obtained.

In Comparative Example 6, the ball deflection is less than 3.0 mm andthe ball has a four-layer construction. As a result, the spin rate onshots with an iron (I #6) rises and a good distance is not obtained.

In Comparative Example 7, the surface hardness of the intermediate layeris higher than the surface hardness of the ball. As a result, the spinrate on shots with an iron (I #6) rises and so the distance is inferior,in addition to which the spin rate on approach shots is low.

In Comparative Example 8, the cover (outermost layer) has a thicknessgreater than 1.0 mm. As a result, the spin rate on shots with an ironrises and the initial velocity of the ball when struck decreases, and sothe distance is inferior.

Japanese Patent Application No. 2020-127860 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A multi-piece solid golf ball comprising a core, an inner envelopelayer, an outer envelope layer, an intermediate layer and a cover,wherein the core is formed of a rubber composition as one or more layer;the inner envelope layer is formed of a resin material as one or morelayer; the outer envelope layer is formed of a resin material as onelayer; the intermediate layer is formed of a resin material as onelayer; the cover is formed of a resin material as one layer having athickness of not more than 1.0 mm; the Shore C hardness at a surface ofthe sphere obtained by encasing the core with the inner envelope layer(inner envelope layer-encased sphere), the Shore C hardness at a surfaceof the sphere obtained by encasing the inner envelope layer-encasedsphere with the outer envelope layer (outer envelope layer-encasedsphere), the Shore C hardness at a surface of the sphere obtained byencasing the outer envelope layer-encased sphere with the intermediatelayer (intermediate layer-encased sphere) and the Shore C hardness at asurface of the ball together satisfy the conditions (Shore C hardness atsurface of outer envelope layer-encased sphere)>(Shore C hardness atsurface of inner envelope layer-encased sphere) and (Shore C hardness atsurface of intermediate layer-encased sphere)>(Shore C hardness at ballsurface); and the ball has a deflection when compressed under a finalload of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) of atleast 3.0 mm.
 2. The golf ball of claim 1 which satisfies the condition:1.0≤(OE vh+IE vh)/Core vh≤4.5, where Core vh is the product of the corevolume (mm³) multiplied by the Shore C hardness Cm at the midpointbetween the core surface and the core center, IE vh is the product ofthe inner envelope layer volume (mm³) multiplied by the Shore C hardnessat the surface of the inner envelope layer-encased sphere, and OE vh isthe product of the outer envelope layer volume (mm³) multiplied by theShore C hardness at the surface of the outer envelope layer-encasedsphere.
 3. The golf ball of claim 1 which satisfies the condition:2.5≤C−B≤5.0, where C is the deflection of the core in millimeters whencompressed under a final load of 1,275 N (130 kgf) from an initial loadof 98 N (10 kgf) and B is the deflection of the ball in millimeters whencompressed under a final load of 1,275 N (130 kgf) from an initial loadof 98 N (10 kgf).
 4. The golf ball of claim 1, wherein the surfacehardnesses of the respective layers satisfy the condition:(Shore C hardness at ball surface)<(Shore C hardness at surface ofintermediate layer-encased sphere)>(Shore C hardness at surface of outerenvelope layer-encased sphere)>(Shore C hardness at surface of innerenvelope layer-encased sphere)>(Shore C hardness at core surface). 5.The golf ball of claim 1, wherein the layers have respective thicknesseswhich together satisfy the condition:(cover thickness)<(intermediate layer thickness)≤(total thickness ofenvelope layer).
 6. The golf ball of claim 1, wherein the layers haverespective thicknesses which together satisfy the condition:(total thickness of envelope layer)/(cover thickness+intermediate layerthickness)≥1.0.
 7. The golf ball of claim 1, wherein the ball has aninitial velocity of at least 76.8 m/s.
 8. The golf ball of claim 1,wherein the core has a diameter and the ball has a diameter whichtogether satisfy the condition:0.65≤(core diameter)/(ball diameter)≤0.80.
 9. The golf ball of claim 1,wherein the core has an internal hardness which satisfies the condition:(Cs−Cm)/(Cm−Cc)≥1.1, where Cc is the Shore C hardness at a center of thecore, Cs is the Shore C hardness at the core surface, and Cm is theShore C hardness at the midpoint between the core surface and the corecenter.